Valve Opening and Closing Event Finalization for Cost Effective Valve Train of Gasoline Engine 2019-01-1191

With more stringent emission norm coming in future, add more pressure on IC engine to improve fuel efficiency for survival in next few decades. In gasoline SI (spark ignition) engine, valve events have major influence on fuel economy, performance and exhaust emissions. Optimization of valve event demands for extensive simulation and testing to achieve balance between conflicting requirement of low end torque, maximum power output, part load fuel consumption and emission performance. Balance between these requirements will become more critical when designing low cost valve train without VVT (Variable valve timing) to reduce overall cost of engine.

Higher CR (Compression ratio) is an important low cost measure to achieve higher thermal efficiency but creates issue of knocking thereby limiting low speed high load performance. The effective CR reduction by means of late intake valve closing (LIVC) is one way to achieve higher expansion ratio while keeping high geometric CR. Due to backflow at low engine speed by late IVC (Intake valve closing) it is challenging to implement late IVC without compromising low end high load performance in absence of VVT.

This study is done using 1-D simulation tool and review of testing data using three pressure analyses. Study include four valve timing points (IVO- Intake valve opening, IVC- Intake valve closing, EVO- Exhaust Valve opening, EVC- Exhaust Valve closing) variation influence on idle stability, idle fuel consumption, part load fuel consumption, WOT (Wide open throttle) performance and exhaust emission. To understand part load fuel consumption P-V (Pressure volume) diagram is analyzed for studying impact of all four timing point on PMEP (Pumping Mean effective pressure) and valve timing is optimized to minimize PMEP while improving gross IMEP (Indicated Mean effective pressure) area.

Objective is to achieve better part load fuel consumption with same power and torque as in current engine using high geometric CR. Challenge was to achieve better low speed high speed torque, maximum power output, low part load fuel consumption and emission without using VVT so as to obtain a cost effective solution. This work presents approach to be used for finalizing valve timing strategy for achieving best compromise in fuel efficiency and engine performance with minimum incremental cost. VVT also has a significant impact on engine out emissions in SI engine that part is not discussed in depth. Fuel efficiency improvement and WOT performance are major discussion points in the paper. Fuel efficiency improvement results directly indicate reduction in the CO2 emission of vehicle.